#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n;
int q[N];

int main() {
	cin >> n;
	for (int i = 0; i < n - 1; ++i) {
		cin >> q[i];
	}
	sort(q, q + n - 1);
	for (int i = 0; i < n - 1; ++i) {
		if (q[i] - 1 != i) {
			cout << i + 1 << endl;
			return 0;
		}
	}
	cout << n << endl;
	return 0;
}